COMPOSITION AND INTERANNUAL VARIABILITY IN TRACE ELEMENT PROFILES OF PACIFIC SARDINE OTOLITHS

Temperature is a primary factor separating Pacific sardine Sardinops sagax into cold and temperate stocks in the California Current Ecosystem. We collected otoliths of age-1 sardine captured in the spring off central California (1996-97) and in the Southern California Bight (SCB; 1991-92 and 1995-2004) where the cold and temperate stocks presumably overlap during seasonal migrations. To assess whether the sardine had distinguishing chemical characteristics, we compared trace element profiles of otoliths with seawater temperatures to evaluate composition and interannual variability. Ca, Mg, P, Sr, Mn, and Ba in dissolved whole otoliths were analyzed by inductively coupled plasma mass spectrometry. Cohorts from central and southern California differed by collection site in Mg/Ca and P/Ca ratios. Mg/Ca and P/Ca ratios covaried and correlated with sea-water temperature in the SCB in most years. High inter-annual variability in some trace element ratios within sites made it difficult to characterize site-specific otolith profiles. Otolith composition was likely influenced by temperature and local conditions. Stock mixing in the SCB may have contributed to interannual variability as well.